Recent years have seen widespread introduction of large rubber tired front end loaders in mining operations previously handled by crawler-type shovel dipper or dragline machines. By "large" reference is made to loader buckets having a capacity of the order of 9-22 cubic yards (or 7-17 cubic meters). Key factors which influenced this trend were considerably lower capital investment, better supplier availability of machines to suit high demands, and more versatility and flexibility in application.
Typical mining applications of front end loaders are stripping overburden and loading of ore or coal. Overburden tends to be a mixture of fines and medium-to-large blocks or slabs of shot material such as sandstone, limestone, basalt, quartz rock mixed with shales and clay. Ores typically are mixtures of fines and small-to-medium sized chunks which are denser than overburden. Coal, which is lighter than overburden in weight, is usually shot and is deposited in veins or seams that many times are multi-seam type separated by overburden partings. The front end loader buckets generally require teeth to dig and load these materials.
In order for a front end loader vehicle to get a load of material in its front-mounted bucket, it must first advance nearly horizontally into the material and then sweep up in an arc under the trapped material. To accomplish this, the bucket and loader encounter the aforementioned material which is difficult to load due to the very extreme variations in size and shape plus weight variations. The chunks or slabs tend to interlock and require high energy to penetrate and prize or lever the material into the bucket. Uneven terrain, which is generally typical, further reduces ease of penetration into the material.
To overcome these many and varied loading obstacles, a front end loader which is propelled through an articulated chassis on rubber tires, moves the bucket hydraulically in an up and down, arc-type or combination direction, producing two types of medium-to-high load forces on the tooth system. First, there is the penetration load form developed as the front end loader and bucket advances into the material being loaded. The variables of material size, weight and location require the teeth to gouge, break out and dig under the material in a fashion analogous to that encountered in a dozer. Second, a jacking or fluttering loading is encountered due to the variables in material shape and location as the teeth are moved up and down to allow both forward and upward bucket penetration through tight openings between chunks, blocks or slabs. More particularly, the jacking or fluttering of the tooth system stems from the sporadic engagement of the teeth with difficult to dislodge material whereby the teeth move up or down or even laterally in order to pass beyond the obstinate material. It will be appreciated that this is not usually uniform across the width of the bucket so that different teeth may be in different fluttering and penetration modes at the same time. Although, the background of the invention is discussed in terms of front end loaders and, more particularly, the jacking operation which characterizes them, such jacking operations have been characteristic of earlier earth moving devices, though generally not as severe. In other words, the problem has existed but had not been brought home to art workers quite as strongly prior to the advent of the large front end loader.
The severity of these jacking forces particularly in front end loaders gave rise to difficulties with conventional excavating teeth, particularly those which consisted of components secured to a vertically extending lock or key.
The vertically extending lock has, and still is, the preferred form for connecting the point and adapter components of the tooth. Inasmuch as the point components, in particular, wear rapidly, replacement is frequent--in some instances, daily. With a vertically extending lock, disengagement of the point from the adapter is easily achieved by merely using a hammer or sledge to pound out the locking pin. In contrast, the horizontally installed locking devices are difficult to remove because there is generally only a short distance between adjacent teeth, thereby limiting the type of drift pin or chisel and hammer or sledge arc--so much so that horizontally locked teeth have become known in the field as "knuckle-busters". Thus, horizontally extending pins were undesirable because of the difficulty of removal. On the other hand, the vertically extending pins were subject to ejection in the jacking mode. The loss of the locking pin (as from severe jacking) constitutes one of the most devastating things that can happen to an excavating tooth. Without the pin, the point generally will come off, exposing the adapter--and, if the machine is not stopped immediately, the adapter can be ruined because it is not intended to be the penetrating component. Even the stoppage is expensive--particularly when unscheduled.
Among the teeth that suffered from this loss of pin drawback were those constructed according to U.S. Pat. Nos. 2,919,506 and 3,079,710. These teeth made use of a combination of special bearing surfaces to absorb severe shock loads and to prevent the development of localized strains and negative thrust, these teeth having been referred to as "stabilized conicals".
Negative thrust tends to pull the point off the adapter. Prior to the 3,079,710 patent, this was resisted by providing a pin lock structure which was characterized by high shear and bearing strength to provide an artificial positive thrust at installation. Such an artificial positive thrust meant extreme difficulty in pin lock removal--thereby frustrating one of the principal objectives of a pin lock: easy removability for replacement while still providing secure locking during working.
The stabilized conical tooth changed the tooth standards--previously the trend was to tighter and tighter fits between the point and adapter to avoid localized strain and negative thrust, and to use bigger and stronger pin locks to resist negative thrust. With the supplemental beam and conical bearing surfaces of the stabilized conical tooth, a most desirable looseness in fit not only could be tolerated--but put to advantage, all while using a light, easily installed and removed pin lock system. Stabilized conical teeth, which had performed brilliantly under all conditions throughout the world for many years started coming apart due to locking pin loss when used on front end loaders. Thus, with the more frequent incidence or severity of the "jacking" stresses, this whole advantageous trend was jeopardized. For example, more frequent loss of pins made the desirable loose fit suspect. Here it should be appreciated that excavating teeth are designed for the exceptional occurrence--the relatively infrequent stress or impact that might destroy the system. If the excavating were always performed in dry sand--the only problem is abrasion. But the manufacturers of excavating equipment, particularly teeth, cannot be sure that a particular piece of equipment may not be moved from a stressless environment to one having high impact loadings. So teeth must be built to withstand the infrequent but severe stresses--the connection of the tooth parts must approach the strength of the connection of the bucket itself.
The stabilized conical tooth point was felt to be the best design because it was rugged, simple, had a relatively massive box section for strength and resistance to corner stresses, had conical bearing surfaces to resist lateral loads, and stabilizing "flats" to resist negative thrust. Yet, with all of this, it was this highly regarded tooth that encountered difficulty in staying together on front end loaders subject to jacking stresses.
The instant invention solved this problem of severe jacking stresses. According to the invention, the vertical pin lock is still used--no need for going to the "knuckle-buster". Further, the real advantage of looseness of fit is still present--contrary to expectation, and along with still being able to use the simple, light-weight pin lock system.
At first this was not felt possible because problems were experienced with the logical approach of making the pin installation more secure. The vertical lock in the stabilized conical tooth was of the corrugated type seen in U.S. Pat. No. 3,126,654. When these teeth encountered pin loss problems, the initial attempts focused on the pin locks themselves--changing the corrugated contour as seen, for example, in U.S. Pat. No. 4,061,432. This improved the situation relative to jacking but was not a complete answer so that in especially difficult cases, return to the horizontal pin lock was considered. The obvious solution to the problem (while still retaining the vertical pin lock) was to deform the pin as in U.S. Pat. No. 2,055,265--but this then created a problem of removal.
As a last ditch effort to avoid going to this unattractive arrangement, tests were performed with a tooth construction not used in excavating but only in dredging. Surprisingly enough, this different arrangement showed promise in solving the pin loss problem due to jacking of front end loader teeth. This was surprising because the dredge teeth were designed for a different function. For example, the forces normally encountered in dredging were generally random and seldom applied at angles greater than 45.degree. to the longitudinal center line. In contrast, the jacking stresses were cyclic and often applied at angles of 80.degree. to the longitudinal centerline.
Further, contra-indicating the use of the dredge tooth structure was the design of the point itself. It had, at the rear of the point, four rearwardly extending tongues--one for each of the top, bottom and sidewalls. The idea of having four rearwardly extending tongues on a point was old as shown by U.S. Pat. No. 1,803,311 and more recently, in U.S. Pat. No. 3,708,895, this being representative of the use of rearwardly extending tongues in the dredge point art. Also representative of the dredge point art is the structure seen in commonly-owned U.S. Pat. No. 4,080,708 where, in addition to the rearwardly extending tongues, the tooth is equipped with internal stabilizing bearing surfaces at the apex of the point socket according to U.S. Pat. No. 3,079,710. It was this 4,080,708 patent structure that showed the promise indicated above. This was unexpected because pin securement was deemed to stem from having a strong structure around the pin--as for example, a continuous section, viz., a box, at the point rear as in U.S. Pat. No. 3,790,353--rather than one that was essentially "weakened" by the removal of metal, in effect, from the box section to provide the tongues.
It is believed that the rearwardly extending tongues, particularly those extending from the top and bottom walls through which the vertical pin extends cooperate in a new manner with the stabilizing flats. These top and bottom tongues, by virtue of the fact that they support the pin independently of the remainder of the box section now can accommodate to the pin shift upon the application of the cyclic forces incident to jacking.
Not only was it necessary to go to a completely contra-indicated point rear end structure (the four tongues) but it was also essential to provide a specific forward part, viz., the dimensional arrangement of the so-called "stabilizing flats". The advantages of a vertically installed pin or keylock can be retained in an excavating tooth which is subject to the severe jacking stresses on a front end loader where the supplemental bearing surfaces are constructed to have a width to length ratio of approximately 2.5 and with the surfaces separated so that the section between surfaces has a width to spacing ratio of approximately 1.8. More particularly, the adapter nose and conforming point socket are defined by forwardly convergent top and bottom walls which terminate in a generally box shaped apex which in turn provides generally parallel stabilizing upper and lower surfaces--each of these surfaces having a width to length ratio of approximately 2.5 and the surfaces separated to obtain a width to thickness ratio of approximately 1.8 thus providing an optimum configuration balancing the considerations of surface area, strength vs. weight and external shape of point.